If you see a meal priced at £20 in the UK, add £2 for 10% tip and £22 is it. Or in a pub, no tip, it's £20 (and £20 in a pub goes a long way on food).

In the US for a meal priced at $20, add $2 for tax (or taxes), add $3.50 for tip, add $2 if they have decided to do valet parking. So it's now $27.50.